1. Field of the Invention
The invention relates to a device for regulating the tension of a thread unwound from a bobbin of a bobbin-holder for a leno selvedge apparatus, said device comprising a brake drum for receiving the bobbin-holder, said brake drum having a brake means and the device being provided with a guide arm for the thread of the bobbin. By way of example, a leno selvedge apparatus is configured as a combination of lifting and half healds. Two lifting healds cooperate thereby with one half heald to produce what is termed a leno selvedge. Such type lifting healds are directly or indirectly secured to the heald frame of a loom. The leno thread is thereby conveyed between half heald and lifting heald, with the stationary thread being passed through the eye of the half heald. As the leno thread alternately moves from one side of the half heald to the other side of the half heald, the weft thread is firmly locked in place together with the stationary thread by the thus produced leno selvedge. The leno selvedge prevents the fabric from fraying in this region.
2. Description of the Prior Art
A device for producing a similar leno selvedge is characterized by two rotating arms that receive at their ends the leno threads, the weft thread being firmly locked in place by the leno threads. This device is also known by the name of “propeller leno device” (EP 0 839 219).
The important point is that the threads that are supplied to the leno selvedge device and that are unwound from a rotating bobbin are in principle always held under a constant and continuous tension. More specifically, the threads are to be prevented from jerking under tension, as delicate threads in particular, glass fiber threads for example, are then likely to break. The risk of such a thread being jerked, which involves the risk of breaking, arises more specifically when, for whatever reason, a tension is applied to the thread, said tension is abruptly slackened and the bobbin continues to rotate, thus forming in a way a thread reserve, which, once used up, causes the thread to be jerked again.
Inasmuch, a device for regulating the thread tension is already known from EP 1 036 228; here there is provided, directly upstream of the leno selvedge device, a holding-down device for the thread which regulates the thread tension already directly upstream of the leno selvedge apparatus. Said holding-down device for the thread is configured to be elastically flexible for the purpose. Disposing this device for regulating the thread tension directly upstream of the leno selvedge device permits to equalize the thread tension under the action of the spring of the holding device when the shed is opened.
The subject matter of the invention now also is a device for regulating the thread tension by equalizing the thread tension directly at the bobbin. Bobbin-holders for rotatably receiving the bobbin are known. Such type bobbin-holders are also known to be provided with brakes that are intended to make sure that the thread is uniformly unwound from the bobbin. It has however been found that the known devices are not always capable of ensuring the uniform unwinding of the thread from the bobbin.